The invention relates to a rotating surgical tool for producing a depression in bone material.
Various rotating tools, for example, drills, milling cutters, reamers, etc., are known for making depressions in bone material. All of these tools are used for producing depressions of different shapes in the bone material, for example, drill holes for receiving bone screws. It is extremely important that these drill holes and depressions be placed in the desired manner in the bone, as in many cases only little bone material is available for fixing bone screws and other parts of implants. For example, in the area of the spine it is extremely difficult to place pedicle screws in the body of the vertebra such that, on the one hand, they are fixed in the desired manner in the body of the vertebra and, on the other hand, do not cause any injuries.
To date, it has essentially been possible for this to be carried out within the operator""s field of vision or, at the most, under radiological supervision, which may have involved increased exposure of the patient and operator to radiation.
The object of the invention is to so design a generic tool that it enables depressions to be made in a controlled manner in the desired position and direction in bone material.
This object is accomplished with a rotating surgical tool of the kind described at the outset, in accordance with the invention, by an ultrasonic transducer being arranged in the surgical tool, the ultrasonic transducer being capable of emitting and receiving ultrasonic waves and being connectable to an ultrasonic generator and a receiver, the receiver generating signals in dependence upon the strength of the ultrasonic radiation received by the ultrasonic transducer and upon the length of time between the emission of ultrasonic radiation and the reception of reflected ultrasonic radiation, the signals being a measure of the condition of the bone material in the direction of emission.
The ultrasonic radiation emitted by the transducer in the rotating tool penetrates the surrounding bone structures and is reflected there, in particular, at the surfaces of the bone material and at inhomogeneities in the bone material, for example, at surfaces at which the structure of the bone material changes. The reflected ultrasonic radiation is picked up by the transducer, and information on the condition of the bone material adjacent to the tool, in particular, on the layer thickness of the bone material and possibly also on structural changes in the bone material, is derivable from the strength of the picked-up signal and the time lapse since emission of the ultrasonic radiation. The operator can use this information to check the position of the tool in the bone and thus the position of the depression made by the tool. Separate transducers may be provided for the emission and reception of the ultrasonic radiation, but it is also possible to emit the ultrasonic radiation and subsequently pick up the reflected radiation again with the same transducer. This can be carried out with, for example, a so-called pulse-echo technique.
It is expedient for the ultrasonic transducer to be arranged in the area of the distal end of the tool so that the area in front of the distal end of the tool is xe2x80x9cseenxe2x80x9d by the ultrasonic radiation emitted by the tool. The operator is thus given information on the condition of the bone material in the cutting direction, and he is thereby enabled to control the direction of advance of the tool accordingly.
A particularly expedient embodiment is obtained when the ultrasonic transducer is arranged in the tool such that the direction in which it emits and receives the ultrasonic waves is at an incline to the axis of rotation, for example, at an angle of inclination of between 30xc2x0 and 60xc2x0, in particular, in the order of magnitude of approximately 45xc2x0. In such an embodiment, the ultrasonic radiation is emitted on the outer surface of a cone which opens in the distal direction, and in this way the operator receives information not only exactly in the direction of advance of the rotating tool but over the entire rotary angle of the tool in an area located in front of the tool in the distal direction. This results in an optimal orientation with regard to the bone areas still to be worked on.
In a preferred embodiment of the invention, provision is made for the tool to comprise an inside receiving space for the ultrasonic transducer, which communicates with a channel extending in the tool as far as the proximal end thereof. Connection lines for the ultrasonic transducer may pass through this channel.
In a preferred embodiment, the tool is a drill with a conical cutting surface, and the ultrasonic transducer is arranged in the area of the conical cutting surface. With such a drill, the operator can see precisely during the drilling operation whether he is at an adequate distance from all delimitations of the bone as the drill advances further, so that the drill hole will definitely extend in the bone material and will not unintentionally penetrate cavities or other tissue.
It is particularly expedient for the tool to comprise a sensor for its angular position, and for the sensor to feed a signal corresponding to the angular position to the receiver which thus generates the signals for the condition of the bone in dependence upon the angular position of the tool. The operator is thus given a comprehensive picture of the condition of the bone material in front of the tool, namely in all angular directions. At the same time, the ultrasonic transducer forms a camera which is arranged on a rotatable carrier and sweeps over the entire area located in front of the tool in all directions.
Provision may also be made for an optical display device which indicates the signals generated by the receiver for the condition of the bone to be associated with the receiver. One can thus read off directly from such a display device the condition of the bone in the direction of emission of the ultrasonic radiation, the available wall thickness of the bone here and any structural changes that might occur.
It is particularly advantageous for cross sections through the tool and the adjacent bone material to be able to be represented on the optical display device, with the condition of the bone material being determined by the signals generated by the receiver. These cross sections simultaneously show the signals generated by the receiver, which occur with a different angular position of the tool, so that one is simultaneously given information on the condition of the bone over the entire angular area.
In particular, provision may be made for the illustrated cross-sectional area to be a conical surface which opens in the distal direction, and the axis of which coincides with the axis of rotation of the tool. A display range which scans the area in front of the tool and thus indicates the condition of the bone in the area which the tool will later penetrate is thus shown.
Cross sections of implants which show the way in which certain implants are to be arranged in the bone after the implantation can also be faded in on the optical display device. With a knowledge of the shape of the implant and the desired position of the implant, it is thus possible for the operator to place depressions, for example, drill holes such that their position corresponds to the shape and position of the implant. The image of the implant can be produced from a data memory in which the data representing this implant are stored. From these data, the image can be superimposed on the image resulting from the ultrasonic signals.
A warning device operating, for example, optically or acoustically can also be associated with the receiver to warn the operator that the wall thickness of the bone material in the area to be worked on is falling below a certain level, i.e., that he risks perforating it.
The following description of a preferred embodiment of the invention serves in conjunction with the drawings to explain the invention in further detail.